In one type of prior accelerometer, a proof mass is mounted to a housing by a flexure hinge, and a force transducer is connected along the accelerometer's sensitive axis between the proof mass and the housing. An acceleration along the sensitive axis results in a compression or tension force on the force transducer. This force is converted into an electrical signal that indicates both the direction and magnitude of the acceleration. The force transducer has a DC and low frequency response, so that the accelerometer is capable of measuring absolute acceleration. Such accelerometers are sometimes referred to as "steady-state" accelerometers, in contrast to "dynamic" accelerometers (e.g., shock and vibration sensors) that typically do not respond to acceleration that changes at a rate less than about 5 Hz. Steady-state accelerometers may be used in navigation, borehole, gravity sensing and related applications in which the measurement of absolute acceleration is required.
In an accelerometer of the type described above, the coefficient of thermal expansion of the force transducer in general cannot be precisely matched by the coefficient of thermal expansion of the proof mass and housing. As a result, the proof mass moves relative to the housing as the temperature changes. This thermally induced movement has a number of adverse effects on the operation of the accelerometer. The flexure hinge resists the thermally induced movement and thereby causes a change in the bias of the instrument. A change in the axis alignment of the accelerometer also occurs as the thermally induced movement causes the position of the center of gravity of the proof mass to change relative to the housing. In addition, the thermally induced movement results in changes in the damping gap and the shock gap clearances between the proof mass and housing, thereby modifying the damping and limiting functions respectively of these components.